diff --git a/torchquantum/algorithm/qcbm.py b/torchquantum/algorithm/qcbm.py
index f4078b90..a5e426a3 100644
--- a/torchquantum/algorithm/qcbm.py
+++ b/torchquantum/algorithm/qcbm.py
@@ -34,7 +34,7 @@ def k_expval(self, px, py):
 
         Args:
 		px: First probability distribution
-			py: Second probability distribution
+		py: Second probability distribution
 
         Returns:
             Expectation value of the RBF Kernel.